PROJECT SUMMARY/ABSTRACT Marijuana is the illicit substance most commonly used in pregnancy; over 200,000 US children are exposed annually. As highlighted by NIDA Director Nora Volkow in the New England Journal, ?our understanding of the long-term effects of prenatal exposure to marijuana in humans is very poor,? yet softening attitudes and legalization efforts are mounting despite lack of evidence of safety in pregnancy. Cohorts from the 1980's suggested neuroteratogenicity, with deficits in executive function and increased aggression in school-age prenatally exposed children; but they did not control for maternal executive function, an important con- founder, relied on self-report of marijuana use leading to exposure misclassification, and did not have ac- cess to modern tools to measure the rapid emergence of executive function in preschoolers. Today's high- er-potency marijuana may also have much greater negative effects. Therefore, a critical, urgent need exists to provide contemporary evidence of the effect of prenatal marijuana exposure on the emergence of execu- tive function and early childhood behavior. Without this knowledge, pregnant women will continue to make risky choices about drug use, and the opportunity to remediate childhood deficits will be missed. Our long- term goal is to document the impact of in utero marijuana on children, to inform policy and guide prevention and intervention. The objective of this application in response to NIDA PAS-14-020 (Public Health Impact of the Changing Policy/Legal Environment for Marijuana) is to fast-track new evidence about the association of in utero marijuana exposure with executive function and aggression at ages 3-6 years. The rationale is that once the impact of prenatal marijuana exposure on development and behavior in contemporary pre- school-age children is known, policy can be informed, and opportunities identified for early intervention. The project will pursue 2 aims: 1) Determine the association of prenatal marijuana with timing and trajectory of emergence of executive function, and 2) Characterize the association of prenatal marijuana and aggressive behavior, by comparing exposed and unexposed children at 3-6 years. The approach will be an efficient, mixed longitudinal-cross sectional study built on an existing pregnancy cohort, where drug use was as- sessed by 3 means: questionnaire, medical record, and urine. Women will be contacted to enroll their child for 1-2 visits to evaluate executive function and behavior. The proposed research is innovative for employ- ing state-of-the-art measures of childhood executive function; for assessing maternal executive function; for prospectively assessing marijuana use by multiple means; for including women with little other illicit drug use to isolate the impact of cannabis; and for assessing outcomes across contexts with multiple informants. This contribution is significant because it will expedite evidence to inform the rapidly changing marijuana policy environment; it will influence personal choices about use in pregnancy; and it will offer hope for early intervention to help prevent academic problems and drug use in adolescence among exposed children.